As with previous betas, the update contains no known issues and can be downloaded via Apple’s Developer page or through the software update tool of the Mac App Store. Build 12F36 asks developers to test PDF viewing and accessibility, along with mobile device management and the standard graphics, Wi-Fi, and wake from sleep functionality. A new seed of Safari 6.1 is also available for developers.

Apple's OS X 10.8.5 beta is being tested alongside the next version of the operating system, OS X Mavericks. Apple has thus far seeded seven Developer Previews of Mavericks and plans to offer the new operating system to the public in the fall.

Not everyone will be able to or will want to spend the money on updating. Not everyone necessarily needs to (despite it potentially being newer/better). Not everyone is using a Mac in an environment where they choose what to install or update to--like a corporate environment--and a brand new version that costs money might not get installed in an environment like that for some time, while some needed security, stability, performance, and general fixes would still be more than welcome for the existing OS that is in use in those environments.

Really, I don't understand all these beta releases for an outgoing operating system…..

If you were in the position of using your Mac for actually getting high performance work done 90% of the time, or if you use some features that Apple simply removed from Mavericks (like custom HiDPI modes for external monitors), then you would understand that there'll be many issues with Mavericks that will keep lots of users with an older, more mature version of the OS like Mountain Lion.

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